1. Field of the Invention
This invention relates to an optical printer used for forming an image on a record medium such as a photosensitive film or the like, for example, in a color video printer or the like and a printer head used therefor, and more particularly to a printer head which includes luminous lines having luminous dots arranged thereon and in which light exposure is carried out while permitting dot-like light from the luminous lines to be superposed on a record medium, to thereby form an image thereon and an optical printer including such a printer head.
2. Discussion of the Background
The assignee proposed an optical printer which is so constructed that a fluorescent luminous tube acting as a luminous element is used as a printer head to form an image on a record medium such as a photosensitive film or the like. The printer head constituted by the fluorescent luminous tube, as shown in FIG. 11, includes a number of luminous dots arranged in two rows in an offset manner. The luminous dots each are formed into a square configuration of sides having a length a. The luminous dots of each of the rows are arranged at intervals a in a main scanning direction. The luminous dots of the rows adjacent to each other are arranged so as to be spaced from each other at pitches P (=a) in the main scanning direction and at a pitch b (=4a) in a sub-scanning direction. The rows are arranged so as to extend in parallel to each other.
The printer heads designated at reference numeral 101 in FIG. 12 each include a box-like envelope, in which a number of anodes each including a phosphor layer are arranged to form luminous dots. An optical printer shown in FIG. 12 includes three such printer heads 101. Luminous dot arrays of each of the printer heads 101 include a main scanning direction defined in a horizontal direction or a direction perpendicular to a plane of FIG. 12 and a sub-scanning direction defined in an upward vertical direction or a vertical direction on the plane of FIG. 12. The luminous dot arrays are arranged in a manner to be parallel to each other at a predetermined interval while keeping positions thereof in the main scanning direction and those in the sub-scanning direction coincident with each other. Dot-like light emitted from the luminous dots of each of the printer heads is directed forwardly in the horizontal direction. The printer heads each are provided on a side thereof facing a substrate with an image-formation optical system 104 constituted of a mirror 102 and a selfoc lens array (SLA) 103, so that a light path of light emitted from each of the printer heads 101 is perpendicularly shifted in a downward vertical direction. The optical printer also includes red, green and blue color filters R, G and B arranged below the selfoc arrays 103, respectively. In the conventional optical printer shown in FIG. 12, the luminous dots of the printer heads 101 each are made of a ZnO:Zn phosphor, which exhibits a considerably expanded luminous spectrum, so that such an arrangement of the color filters R, G and B permits dot-like light of each of red, green and blue luminous colors to be irradiated onto a record medium 105 which is arranged below the color filters R, G and B. The record medium 105 is arranged so as to be moved in the sub-scanning direction or a lateral direction in FIG. 12 relatively to dot-like light emitted from each of the printer heads 101.
During a recording operation, the record medium 105 is moved in the sub-scanning direction relatively to light emitted from the printer heads 101. Data on an image decomposed into red, green and blue colors are fed to the printer heads 101 corresponding in color thereto, so that the two-row luminous dots of each of the printer heads 101 are driven for luminescence at predetermined timings in synchronism with relative movement of the record medium 105 described above. Such driving permits light emitted from the luminous dots arranged in two rows and in an offset manner to be irradiated in the form of a single straight line parallel to the main scanning direction on the record medium 105, so that irradiation of light beams from the printer heads 101 to the printer head 101 while being superposed on each other leads to formation of a full-color image on the record medium 105.
The selfoc lens arrays 103 of the image-formation optical system described above, as shown in FIG. 13, form an erected real image of an equi-magnification on the record medium 105. Thus, dot-like light emitted from the luminous dots forms the image on the record medium 105 without changing a configuration thereof or while keeping the configuration unvaried.
In order to increase the quantity of light in the conventional optical printer or printer heads constructed as described above, it would be considered to increase an anode voltage of the printer head or arrange two or more printer heads of the same luminous color. Unfortunately, an increase in anode voltage of the printer head requires to increase dielectric strength of a driver IC for driving the printer head, leading to an increase in manufacturing cost of the printer head. Also, such an increase in the number of printer heads as described above likewise causes an increase in manufacturing cost. Thus, the approaches each are an obstacle to a reduction in manufacturing cost, resulting in failing to be successfully employed to increase manufacturing cost.
In particular, the optical printer including the printer heads respectively exhibiting red, green and blue luminous colors has a disadvantage that the red luminous color is generally decreased in light quantity or intensity as compared with the green and blue luminous colors, so that a full-color image formed is deteriorated in color balance, leading to a failure in reproduction of natural color. This would be due to the fact that a red color ingredient contained in light emitted from the ZnO:Zn phosphor is reduced in light intensity as compared with the remaining color ingredients.